1. Field of the Invention
This invention includes to a semiconductor light emitting device and an optical recording and/or reproducing apparatus.
2. Description of the Related Art
Light may be amplified by stimulating the emission of radiation having discrete frequencies from incident electromagnetic radiation of mixed frequencies. In a light emitting device such as a semiconductor laser, especially in AlGaInP semiconductor lasers, it is difficult to make a sufficiently high barrier of heterojunction between the active layer and the cladding layer, impurity doping control technologies seriously affect the device characteristics.
More specifically, there are known AlGaInP semiconductor lasers using known cladding layers near the active layer by controlling the impurity doping position during the manufacturing process. Conventional AlGaInP semiconductor laser having non-doped cladding layers near the active layer are advantageous in preventing diffusion of impurities from the cladding layers.
These conventional AlGaInP semiconductor lasers, however, involve some problems. Namely, if the impurity doping position is remote from the active layer, then the efficiency of converting an injected current into light decreases, and the operation current increases. In contrast, if the impurity doping position is nearer to the active layer, diffusion of impurities reach the active layer by the annealing process and so on, and deteriorates the device in a short time as short as several hours. This results in shortening the life of the device and decreasing the reliability of the device.
Thus, the conventional AlGaInP semiconductor laser needs to control impurity doping with high accuracy, so there is difficulty in its manufacturing.
It is therefore an object of the invention to provide a semiconductor light emitting device which is improved in emission efficiency, operative with a low current, improved in reliability, and can be manufactured easily, and to provide an optical recording and/or reproducing apparatus using the semiconductor light emitting device as is light source.
According to the first aspect of the invention, there is provided a semiconductor light emitting device having a structure including an active layer between a p-type cladding layer and an n-type cladding layer on a base body, comprising:
at least one of the p-type cladding layer and the n-type cladding layer has a lattice mismatch relative to the base body not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924.
According to the second aspect of the invention, there is provided a semiconductor light emitting device having a structure including an active layer between a p-type cladding layer and an n-type cladding layer on a base body, comprising:
at least one of the p-type cladding layer and the n-type cladding layer, and the active layer have a lattice mismatch relative to the base body not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924.
According to the third aspect of the invention, there is provided a semiconductor light emitting device having a structure including an active layer between a p-type cladding layer and an n-type cladding layer on a base body, comprising:
the p-type cladding layer, n-type cladding layer and active layer are in lattice mismatch with the base body.
According to the fourth aspect of the intention, there is provided an optical recording and/or reproducing apparatus using as a light source thereof a semiconductor light emitting device having a structure including an active layer between a p-type cladding layer and an n-type cladding layer on a base body, comprising:
at least one of the p-type cladding layer and the n-type cladding layer has a lattice mismatch relative to the base body not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924.
According to the fifth aspect of the invention, there is provided an optical recording and/or reproducing apparatus using as a light source thereof a semiconductor light emitting device having a structure including an active layer between a p-type cladding layer and an n-type cladding layer on a base body, comprising:
at least one of the p-type cladding layer and the n-type cladding layer, and the active layer have a lattice mismatch relative to the base body not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924.
When the semiconductor layer stacked on the base body has a lattice mismatch with respect to the base body, the degree of the lattice mismatch xcex94a/a is expressed as xcex94a/axe2x89xa1(a2xe2x88x92a1)/a1 where a1 is the lattice constant of the base body, and a2 is the lattice constant of the semiconductor layer. In the present invention, the degree of the lattice mismatch is determined from the viewpoint of effectively preventing diffusion of impurities and from the view point of preventing dislocation in the crystal to be not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924, for example, or more preferably, not smaller than 3.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x923.0xc3x9710xe2x88x924.
In the first and fourth aspects of the invention, the lattice mismatch may be either substantially even or uneven within the p-type cladding layer or the n-type cladding layer. In the second, third and fifth aspects of the invention, the lattice mismatch may be either substantially even or uneven within the p-type cladding layer, n-type cladding layer or active layer, or it may be substantially even among the p-type cladding layer, active layer and n-type cladding layer.
In the first, second, fourth and fifth aspects of the invention, one of the p-type cladding layer and the n-type cladding layer may include lattice mismatch, or both of them may include lattice mismatch. In the present invention, if both the p-type cladding layer and the n-type cladding layer include lattice mismatch, lattice mismatch of the p-type cladding layer with respect to the base body may be not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923, and lattice mismatch of the n-type cladding layer with respect to the base body may be not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924. The semiconductor light emitting device may include a first optical guide layer between the p-type cladding layer and the active layer and a second optical guide layer between the n-type cladding layer and the active layer. In this case, at least one of the first optical guide layer and the second optical guide layer may have lattice mismatch with respect to the base body in the range not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924.
In the present invention, the semiconductor light emitting device is typically an AlGaInP semiconductor light emitting device, and a GaAs substrate, for example, is used as the base body.
According to the first, second, fourth and fifth aspects of the invention, at least one of the p-type cladding layer and the n-type cladding layer has lattice mismatch with respect to the base body within the range not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924, or at least one of the p-type cladding layer and the n-type cladding layer, and the active layer have lattice. mismatch with respect to the base body within the range not smaller than 2.0xc3x9710xe2x88x924 and not larger than 3.0xc3x9710xe2x88x923 or not smaller than xe2x88x921.5xc3x9710xe2x88x923 and not larger than xe2x88x922.0xc3x9710xe2x88x924. Therefore, diffusion of impurities in the p-type cladding layer or in the n-type cladding layer can be prevented. As a result, impurities in the p-type cladding layer or in the n-type cladding layer from diffusing into the active layer.
According to the third aspect of the invention, the active layer, p-type cladding layer and n-type cladding layer have lattice mismatch with respect to the base body. Therefore, diffusion of impurities in the p-type cladding layer or in the n-type cladding layer can be prevented. As a result, impurities in the p-type cladding layer or in the n-type cladding layer from diffusing into the active layer.
Still unknown are details of the mechanism of preventing diffusion of impurities in cladding layers. Presumably because the energy of the system is lower when group II impurities in the cladding layers having plus lattice mismatch with respect to the GaAs substrate, for example, diffuse in the opposite direction from the GaAs substrate rather than diffusing toward the substrate and when group VI impurities in the cladding layer having minus lattice mismatch with respect to the GaAs substrate diffuse toward the GaAs substrate rather than diffusing away from the substrate, it might result in preventing diffusion of impurities from cladding layers into the active layer. Alternatively, it is possible that migration energy of impurities is high in cladding layers having plus or minus lattice mismatch with respect to the GaAs substrate, and it results in preventing diffusion of impurities. It is also presumed that, in a cladding layer having plus lattice mismatch with respect to the GaAs substrate, the density of group III holes assisting diffusion of group II impurities replacing group III atoms to become acceptor impurities or group IV impurities replacing group III atoms to become donor impurities decreases, and in a cladding layer having minus lattice mismatch with respect to the GaAs substrate, the density of group V holes assisting diffusion of replacing group V atoms to become donor impurities decreases, and it results in preventing diffusion of impurities.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.